High-frequency transmission system



Oct. 18, 1949. w. E. BRADLEY HIGH-FREQUENCY TRANSMISSION SYSTEM OriginalFiled Aug. 30, 1944 D A. O L O T OSCILLATOR INVENTOR 7 WILLIAM E.BRADLEY ATTORNEY Patented Oct. 18 1949 HIGH-FREQUENCY"TRANSMISSIONSYSTEM William E. Bradley,. Swarthmore, Pa., assignor, by mesneassignments, to Philco Corporation, Philadelphia, Pa a corporation ofPennsylvania Original. application August 30, 1944, Serial No. 551,951.Divided-and this. application August 31, 1944, Serial No. 552,115.

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This application, which is a division of application Serial No. 551,951,filed August 30, 1944, relates to a frequency stabilizing system andmore particularly relates to a system for adjusting and stabilizing thefrequency of high frequency oscillators as the voltage, current or loadimpedance varies.

In accordance with my invention, frequency stabilization is effected byreflecting a reactance into the line, in response to a shift infrequency from normal, of a kind that will tend to restore the frequencyto its original value.

More specifically, in one form of my invention I connect a parallelreactance resonant to the frequency to. be controlled across thetransmission line. There are a number of points along the transmissionline one half. wave lengthapart, where an inductive reactance applied tothe transmission circuit will elevate and a capacitative reactance willlower the frequency of the oscillator. At one of these points where thiseffect is maximum, I shunt my parallel resonant circuit across thetransmission line which matches the impedance of the load.

If now the load impedance so changes that the frequency rises, acapacitance is presented by the parallel resonant circuit to thetransmission line which lowers the frequency almost to its normal value.

If the load impedance so changes thatthe frequency falls, inductance ispresented to the transmission line which raises the frequency almost toits normal value.

Halfway between the points along the transmission line referred toabove, an inductive reactance will lower and a capacitative reactancewill elevate the frequency. This reactance is secured by a resonantseries inductance and capacitance connected in series in the systematone of these half Way points.

If the frequency rises in response to a change in load impedance abovethe stabilizing value and therefore above resonance frequency, aninductance is presented by the series resonant circuit to thetransmission line which lowers the fre- Accordingly, an object of myinvention is to provide a novel network arrangement for effectingfrequency stabilization of a system.

A further object of my invention is to provide a novel reactance networkcoupled to a circuit, the reactance reflected into the oscillatingcircuit being a function of the frequency fluctuations from normal tomaintain the frequency of the system substantially constant.

Still another object of my invention is to provide a novel resonantparallel inductance capacitance circuit so connected in a transmissionsystem that it presents capacitance to the line when the frequency risesto lower the frequency to normal and presents inductance to the linewhen the frequency drops to raise the frequency to normal.

Another object of my invention is to provide a novel resonant seriesinductance capacitance circuit so connected in a transmission systemthat it. presents inductance to the line when the frequency rises tolower the frequency to normal and presents capacitance to the line whenthe frequency drops to raise the frequency to normal.

Still a further object of my invention is to provide a novel frequencycontrolled stabilizer which tends to maintain the load impedancesubstantially constant.

These and other objects of my invention will appear from the detaileddiscussion which follows in connection with the drawings, in whichFigure 1' shows an arrangement for connecting a wave guide in series incarrying out my invention.

Figure 2 shows an arrangement for connecting a wave guide in parallel incarrying out my invention..

Figure 3 shows in cross-section a specific construction of wave guideembodying my invention.

Referring now to Figure 1, I have shown a main and branch wave connectedin series. Here the main wave guide 51 is a hollow tube of metal ofrectangular cross-section and is connected at one end to an oscillatorwhich may have two or more modes of oscillation such as a magnetron. Theopposite end of the line is connected to a fluctuating impedance load.The wave guide is designed to carry the transverse electric mode withthe. lines of electric field parallel to the narrow dimension of theguide. The branch guide 52 of similar rectangular cross-section is anintegral munber of half wave lengths long opening into a cut in thelarge dimension of the main guide at the junction 5'4 and is closed atthe end 53.

All the longitudinal current in the main guide must then flow in thebranch guide and this arrangement is spoken of as a series connection.The coupling junction 54 of the branch guide 52 to the main guide 5| isat such a point along the main guide that an increase in the effectivecapacitance of the load as viewed from this junction would cause thefrequency to rise, and an increase in inductance lowers the frequency.

In order to secure this result, the distance from the junction 54 to theend of the branch wave guide 52 at its closed end 53 is made one halfwave length. The impedance looking into this branch guide from the mainwave guide is substantially a short circuit when the stabilizingfrequency exists and the stabilizing unit has no effect upon atransmission through the main wave guide from the oscillator to theload.

If the impedance of the load is changed so that the impedance lookinginto the main wave guide at junction 54 appears to have a capacitanceadded to it, the frequency of the oscillator will rise.

As the frequency begins to increase, the impedance looking into thecompensator no longer appears as a short circuit; instead it appears tobe an inductance. This inductance acts in series with the equivalentcapacitance seen looking totion an odd number of quarter wave lengthslong i shown in Figure 2. Here the main wave guide 6| is jointed at 62to a branch wave guide 63 at a cut in both along the narrow edge of theguide providing a shunt connection. The junction here selected is halfway between the junction available to be used for Figure 1 in relationto the oscillator and are those positions on the main wave guide 6Iwhere the addition of a capacitance lowers the frequency a maximumamount and the addition of inductance raises the frequency.

The end 64 of the stub or branch guide 63 is closed off so that itpresents an infinite impedance to the main wave guide 6| at normalfrequency.

If now theload is changed so that the frequency tends to decrease, thisstub line operates as a less than quarter wave line, and thus operatesto add inductance to the line and therefore to raise and restore thefrequency to it normal value.

Because of its position on the line, its action counteracts the changein load impedance. Conversely, if the load impedance so changes that itacts as an inductance at the junction point of the main line and stuband the frequency rises, the stub line operates as a greater thanquarter wave line and thus adds capacitance to the line causing thefrequency to restore itself.

A specific arrangement of my invention using wave guides is shown inFigure 3 in cross-section. This is a modification of Figure 1, the crosssection being taken through the narrow width of the wave guide. Thecoupling junction IOI of the branch guide I02 to the main guide I03 isat such a point along the main guide that an increase in the effectivecapacitance of the load as viewed from this junction point would causethe frequency to rise. At the normal frequency, the branch guide systempresents a short circuit to the main guide at junction MI. in order thatthis may be so, the distance from junction IN to junction I04 is madeclose to a quarter wave length. An open circuit at junction I04 wouldappear as a short circuit at junction IOI because of the well knownimpedance inversion properties of a quarter wave length of wave guide.At junction I04 the two sub-branches I05 and I06 are in series becausethey are joined along their broad faces. The impedance looking intosub-branch I05 is a resistance, because I05 is partially filled with alossy material I01 which absorbs any energy which enters I05 at I04. Asviewed from I04, sub-branch I06 appears to have whatever impedance ispresented to it at junction I08 by cavity resonator I09, because of thewell known impedance retaining property of the half wave length sectionof guide between I04 and I08. At the normal frequency, this cavityresonator is tuned by adjusting screw IIO, which may be placed almostanywhere in the wall of the cavity, o that the impedance of the cavityas seen from junction I08 is infinite. Then the impedance of section I06as seen from I04 is infinite, and the series addition of I05 is of noimportance.

Consequently, the impedance as seen from junction IOI is zero. When thefrequency is slightly raised, the impedance transformation properties ofthe wave guide sections do not change very much. However, the impedanceof the cavity becomes a high capacitive reactance, which then places ahigh capacitive reactance in series with the lossy sub-branch I05 atjunction I04. Again, the impedance of the lossy subbranch isinsignificant compared to the impedance in series with it, so theimpedance as viewed from junction IOI becomes an inductive reactancebecause of the impedance inversion qualities of a quarter wave guidesection. This is just what is needed in order that the regulatory actiondescribed in connection with Figure 2 may become effective. Atfrequencies far removed from normal, the impedance of the cavity asviewed from I08 becomes low, so the impedance as viewed from junctionI04 becomes substantially the impedance of the lossy sub-branch I05.Consequently, a resistive impedance is presented to the main guide at IMand the load is not disconnected, as it would be if the lossy guidesection I05 were absent.

Experimental work with frequency stabilizers of this type indicate thatthey are also effective in reducing the frequency change caused byvariations in voltage or current in the oscillator tube. They findapplication in radar systems where reflected waves, such as may comefrom the antenna housing, effect an impedance change in the antennaload.

- Various modifications of the principles of my invention will now beevident to those skilled in the art. I therefore prefer not to be boundby the specific disclosures hereinabove set forth, but only by theappended claims.

I claim:

1. In a wave guide transmission system for connecting a source of highfrequency to a load whose impedance changes, a main rectangular waveguide, a branch wave guide an integral number of quarter wave lengthslong opening into a cut in the large dimension of the main wave guide, astub wave guide opening into a out along the large dimension of saidbranch wave guide an odd number of quarter waves length from said firstmentioned opening, said stub wave guide being partially filled withlossy material and a cavity resonator connected to the opposite end ofsaid branch wave guide from the first mentioned open end, said cavityhaving infinite impedance at the frequency to be stabilized.

2. In a wave guide transmission circuit, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said wave guide, said wave guide having a number of pointstherealong one-half wave length apart where reactance can be reflectedinto said oscillator in response to a shift in frequency from apredetermined value to restore the frequency of said oscillator to thepredetermined value, and a frequency stabilizer comprising a stub an oddnumber of quarter waves long at the frequency to be controlled connectedin parallel with said Wave guide at a position along said guide wherethe addition of capacitance lowers the frequency of said oscillator.

3. In a wave guide transmission circuit, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wage guide, a load whose impedance changes connected to theother end of said wave guide, said wave guide having a number of pointstherealong one-half wave length apart where reactance can be reflectedinto said oscillator in response to a shift in frequency from apredetermined value to restore the frequency of said oscillator to thepredetermined value, and a frequency stabilizer comprising a stub an oddnumber of quarter waves long at the frequency to be controlled connectedin parallel with said. wave guide at a position along said guide wherethe addition of capacitance lowers the frequency of said oscillator,said stub being less than a quarter of the wave length at a frequencybelow the desired oscillation frequency.

4. In a wave guide transmission circuit, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said wave guide, there being a number of points along saidtransmission line one-half wave length apart where the addition ofcapacitive reactance applied to the line will lower the frequency ofsaid frequency source, and a frequency stabilizer comprising a stub anodd number of quarter waves long at the frequency to be controlledconnected in parallel with said Wave guide at a position along said waveguide where the addition of capacitance lowers the frequency of thecircuit, said stub in response to a rise in frequency being greater thanan odd number of quarter waves long.

5. In a wave guide transmission system, a rectangular wave guide, amagnetron oscillator having two or more modes of oscillations connectedto one end of said wave guide, a load whose impedance changes connectedto the other end of said wave guide, there being a number of pointsalong the transmission line one-half wave length apart whose capacitivereactance applied to the line will raise the frequency of said frequencysource, and a frequency stabilizer comprising a branch guide having across-section similar to that of said wave guide connected in seriestherewith, said branch guide being connected at a point along said mainguide where the addition of capacitance raises the frequency of saidoscillation, and a stub wave guide opening into a out along the largerdimension ofsaidbranch wave guide an; odd number of quarter wave lengthsfrom said first mentioned connection of said: branch wave guide.

6. In a wave guide transmission system, a wave guide, a magnetronoscillator having two ormore modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said wave guide, there being a number of points along thetransmission line one-half wave length apart whose capacitive reactanceapplied to the line will raise the frequency of said frequency source,and a frequency stabilizer comprising a branch guide having across-section similar to that of said wave guide connected in seriestherewith and being a half wave length long at the frequency to becontrolled, said branch guide being connected at av point along saidmain guide Where the-addition of capacitance raises the frequency ofsaid oscillator, said branch guide in response to a drop in frequencypresenting capacitance to raise the frequency of said oscillator.

'7. In a wave guide transmission system, a rectangular wave guide, amagnetron oscillator having two or more modes of oscillations connectedto one end of said wave guide, a load whose impedance changes connectedto the other end of said wave guide, and a frequency stabilizercomprising a branch guide having a cross-section similar to that of saidwave guide connected in series therewith and being a half wave lengthlong at the frequency to be controlled, said branch guide beingconnected at a point along said main guide where the addition ofcapacitance raises the frequency of said oscillator, said branch guidein response to a rise in frequency presenting inductance to lower thefrequency of said oscillator, and a stub wave guide opening into a cutalong the large dimension of said branch wave guide an odd number ofquarter wave lengths from said first mentioned connection of said branchwave guide, said stub Wave guide being filled with lossy material.

8. In a wave guide transmission system, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said wave guide, there being a number of points along saidwave guide one-half wave length apart where an inductive reactancereflected into said oscillator will lower and a capacitive reactancereflected into said oscillator will raise the frequency of saidfrequency source, and a frequency stabiilzer comprising a rectangularbranch guide an integral number of half waves length long opening into acut in the large dimension of the main guide and closed at its otherend, said branch guide being connected to said wave guide at a pointwhere inductive reactance most lowers the frequency and capacitativereactance most raises the frequency of said oscillator, and a stubpresenting a series resistance connected to said branch wave guide.

9. In a wave guide transmission system, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said Wave guide, there being a number of points along saidwave guide one-half wave length apart where an inductive reactancereflected into said oscillator will lower and a capacitive reactancereflected into said oscillator will raise the frequency of said to saidmain wave guide along the narrow edge of .the wave guide and closed atits other end, said branch wave guide being connected to said main waveguide at a point where inductive reactance most raises the frequency andcapacitative reactance most lowers the frequency of said oscillator.

10. In a wave guide transmission system, a wave guide, a source of highfrequency oscillations whose frequency is subject to fluctuations inresponse to changes in load impedance and having two or more modes ofoscillations, said source being connected to one end of said wave guide,a load 'whose impedance changes connected to the other end of saidwaveguide, said wave guide connecting said source of energy to saidload, said wave guide having a number of points therealong one-half wavelength apart where reactance can be reflected into said oscillator inresponse to a shift in frequency from a predetermined value to restorethe frequency to the predetermined value, and a frequency stabilizercomprising a stub having a length related to the frequency of theoscillator and connected to the main wave guide at a point at which itpresents reactance to said oscillator which compensates for the shift inreactance of the load to maintain the operating frequency of saidoscillator substantially constant.

11. In a wave guide transmission system, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said wave guide, said wave guide having a number of pointstherealong one-half wave length apart where reactance can be reflectedinto the line in response to a shift in frequency from a predeter-emined value to restore the frequency to the predetermined value, and afrequency stabilizer comprising a stub having a length related to thefrequency of the oscillator and connected to the main wave guide at apoint along said wave guide at which an increase in the effectivecapacitance of the load as viewed from the junction would cause thefrequency of said oscillator to rise, the stub being of a length topresent a short circuit to the main wave guide at said junction.

12. In a wave guide transmission system, a wave guide, a magnetronoscillator having two or more modes of oscillations connected to one endof said wave guide, a load whose impedance changes connected to theother end of said wave guide, the frequency of said source being subjectto fluctuations in response to changes in load impedance, a branch waveguide an integral number of quarter wave lengths long opening into a cutin the large dimension of the main wave guide at a point along said waveguide at which an increase in the effective capacitance of the load asviewed from the junction would cause the frequency of said oscillator torise, the branch being of a length to present a short circuit to themain wave guide at said junction.

WILLIAM E. BRADLEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Date

